1. Field of the Invention
The present invention relates generally to the field of semiconductor manufacturing. More specifically, the present invention relates to a method of on-site cleaning gas, e.g., F.sub.2, generation for semiconductor and/or flat panel display process chamber cleaning, and a method of eliminating HF from F.sub.2 generator by, for example, cryo condensation.
2. Description of the Related Art
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a layer or film on a substrate. As is well known in this art, such a layer can be deposited by chemical vapor deposition (CVD). In a conventional plasma-enhanced CVD (PECVD) processes, a controlled plasma is formed using radiofrequency (RF) energy or microwave energy to decompose and/or energize reactive species in reactant gases to produce the desired film.
One problem that arises during such CVD processes is that unwanted deposition occurs on some or all of the processing chamber's interior surfaces, leading to potentially high maintenance costs. With CVD of a desired film onto a substrate, the deposition of undesired residues can occur on any surface, because the reactive gases can diffuse to most parts of the processing chamber, even between cracks and around corners. During subsequent substrate depositions, these residues can accelerate until a continuous film is grown on the undesired parts. Over time, failure to clean the residue from the CVD apparatus often degrades process yield.
When excess deposition starts to interfere with the CVD system's performance, various parts of the chamber can be replaced to remove unwanted accumulations thereon. However, the replacement would potentially increase the maintenance cost. Moreover, such maintenance adversely affects throughput of the CVD system. Therefore, cleaning of the processing chamber is regularly performed to remove such unwanted residues from the chamber walls, heater, and other process kit parts.
Commonly performed between deposition steps for every substrate (or every n substrates), in situ cleaning procedures using one or more cleaning (i.e., etchant) gases are performed to remove the unwanted residual material accumulated during the deposition process. Common cleaning techniques known to those having ordinary skill in this art include thermal, RF plasma, and microwave plasma techniques.
A radiofrequency plasma cleaning process could use nitrogen trifluoride (NF.sub.3), for example, because such a technique is capable of imparting the high energies required to dissociate a more stable compound. First, NF.sub.3 is flowed into the processing chamber being cleaned. Radiofrequency energy is then applied (e.g., via the substrate processing system's capacitively coupled electrodes), thus generating the fluorine radicals (F*) which remove the unwanted residues from the processing chamber's components. A frequency of 13.56 megahertz (MHz) is commonly used to excite the plasma.
However, the radiofrequency plasma process using NF.sub.3 could be costly, as NF.sub.3 is very expensive. Other gases such as SF.sub.6 and C.sub.2 F.sub.6 are cheaper, but usually cause significant environmental pollution. Therefore, the prior art is deficient in the lack of effective and economic means of cleaning a semiconductor and/or flat panel display process chamber with minimal environmental pollution. Specifically, the prior art is deficient in the lack of effective means of cleaning a process chamber by generating the cleaning gas, such as, F.sub.2 on site and further delivering the cleaning gas to the chamber so that the HF is eliminated from the F.sub.2 generator by cryo condensation. The present invention fulfills these long-standing needs and desires in the art.